Add classes to Gravity Forms fields based on the type of field (i.e. address, name, email, etc.) In functions.php

gravityforms.txt

// Add field type class to Gravity Forms fields
add_filter( 'gform_field_css_class', 'gf_field_type_classes', 10, 3 );
function gf_field_type_classes( $classes, $field, $form ) {
    $classes .= ' gfield_' . $field->type;
    return $classes;
}